Volume control circuits



T. M. SHRADER VOLUME CONTROL CIRCUITS Filed Nov. 12, 1938 Nov. 18, 1941.

jNVENToR. TERRY M. SHRADER ATTORNEY.

Patented Nov. 18, 1941 VOLUME CONTROL cino'u'irs Terry M. Shrader, West Summit, NrJ., assignor to Radio Corporation of America, a corporation of Delaware Application November 12, 1938',` Serial No. 240,027

9 Claims.

My present invention relates in general to volumev control circuits, and more specifically to volume control circuits for audio amplifiers.

In the past, amplifiers have been provided with signal grids of the variable mu type. Upon this grid was impressed the signal voltage; and' the gain control bias was also applied to such grid. However, and particularly at audio frequencies, there exists the problem of designing the signal grid so as to impart a characteristic to the amplifier whereby the very high signals can be handled without considerable distortion and high plate current. In one attempted solution of this diiculty the amplier is provided with an auxiliary gain control grid (so-called hexode tube) while the signal is applied tothe usual signal grid. The same dimculties are encountered in this case; in addition, distortion, due to kinks in the mutual' conductance curve of the tube, is produced when the signal is applied to a grid located further'away from the cathode than the gain control grid.

Now I have discovered a method of overcoming the aforesaid problem, and it is one ofthe main objects of my present invention to provide a means for utilizing the method; the latter including the steps of degenerating the signal input circuit of an amplifier, as the signal ampli-y tude increases, to decrease the output of the amplifier, and concurrently decreasing the current flow through the output circuit of the latter.

Another important object of this invention is to provide a wave transmission tube 'which is so constructed that degeneration can be introduced into the wave input circuit to prevent overswinging of the wave input electrode and reduce distortion; the electron flow to the output electrode of the tube being reduced substantially at the same time to provide an auxiliary effective control over the output intensity' of the tube.

Still another object of my invention is toprovide an audio amplifier which includes a tube having a signal grid, an output electrode, an electron diversion electrode and a control means; the control means acting to regulate the distribution of electrons between the diversion electrode and the output electrode, and the current flow through i the circuit of the diversion electrode providing signal voltage which is fed back to the signal grid in degenerative phase,

Still other objects of my invention are to improve generally thesimplicity and efficiency of audior amplifier gain control circuits, and more especialy to provide audio volume control circuits which are reliable in operation and economical to manufacture and assemble.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims; the invention itself, however, as to both its organization and method vof operation will best be understood by reference, to the following description taken in connection with the drawing in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In Athe drawing Fig. 1 shows an audio amplifier embodying one form of the invention,

l Fig. 2 shows a modification,

Fig. 3 illustrates a further embodiment,

t. Fig. 4 shows still another form of the invenion.

Referring now to the accompanying drawing, whereinlike reference characters in the different figures denote similar circuit elements, there is depicted in Fig. 1 a wave amplifier network employing a heXode type tube l which is provided with a cathode 2a plate 3 and four successive grids,r4,15, 6 and 1. The cathode is established at a fixed potential, for example at ground potential, VThe source of wave, or signal, energy (not shown to vpreserve simplicity of disclosure) is connected from signal grid 4 to ground through a path including a resistor 8 in series with the grid biassource 9. The output, or plate, electrode 3 is connected to the grounded cathode through a path including the output, or utilization, circuit (not shown) and the positive potential sourcel l0.

`Grid 5, lthe electron-diversion electrode, is connected tothe positive terminal of source l0 by a resistive impedancev Il. The condenser l2 connects the electrode end of impedance Il to the grid end of resistor 8. Since the impedance Il is unbypaussed at signal frequencies, there will be developedvsignal voltage across the impedance when current V flows through the latter. Such signal voltagewill `be impressed upon grid 4 in degenerative phase to thesignal voltage from the signal source. Hence, thefunction of electrode Sisto-introduce degeneration into the signal inputv circuit of the amplifier. Grid 'l acts as a screen grid electrode, and is connected to the positive terminal of source Ill.` The grid 6, disposed between electrode k5 and plate 3, has ap,

plied to it a direct `current potential of variable magnitudethereby to regulate the distribution of'Y electrons between electrode 5 and plate 3. For example, grid 6 is shown connected by lead I3 and adjustable tap I4 to source Q It will be clear that'as the tap I 4 is adjusted to the negative terminal of potential source 9, the electrode 6 will become increasingly negative and thereby cause more electrons to flow to electrode 5 than to plate 3.

,If' the negative potential appli-ed to gri-d 6 is ofsuiiicient value to cause all of the electrons, normally flowing to the plate 3, to llow to electrode 5, the result will be that the signal input circuit will be highly degenerated. The degenerative signal voltage introduced into the signal input circuit may be said to @buck out most of the inputl signal voltage therebyv preventing overswinging the signal gridv4. Furthermore, itis. to, be noted that when grid 6 has a bias sufficiently high to cut off the plate current ow, the compe bined action of the degenerative f ee lbac-l/:Mand4 the cut-off of plate current will result-fin' :re-

ducing the volume to Zero. substantially no bias is applied to grid 6, theeleptroll11W.,V 9;.

electrode 5 is low, and is preferably very low for maximum gain, and hence, veryy little, deg.

generation is introduced into Ythev signal input circuit. Furthermore, the plate current- 110W` in the last' vnamed case will be av maximuni,y and, therefore, the volume ofthe amplifier Willalso be a' 1naxirr 1um.` Thev signal, of'coursag'is veryI small when maximumv gain is neededfso there is Vno'over-sWingim-g of; the signal 4V.'v 'Not only does the introduction ofdegeneration'prevent over-swinging of the signal grid, butadisktortion is preventedby virtue of the degenerative feedbackas is Well known by those vskilled,injtthe art.

It will, therefore, be appreciated-thatthepresent volume control methodembodiesV the'dualgregula.

tion of plate current as well as degenerative feedback to thev signal input circuit.`

In Figt 2 there is shown the invention appliedl to. an audio.` amplifier which may embody a tube 'I'Y of the A-'tvpe The difference between this type of-tube and that shown in' Fig. 1 resides' in the 'fact4 that an auxiliary screen gridv electrode'lf'v is disposedbetween the Vgain congtrol'grid 6 and the electrode 5. Furthermore,... the electrode 5in the 6A8 type tubev actually consists of a pair of spacedside rods, as'thosev skilled inthe art Well know. Such a tube has the advantage Aof-havi11g-thfe electrodeS draw very low 'current when no biasis applied -to electrode 6i 'Ihe audio signal input source is shown as com prising a diode detector I 5, and theanodejthereof is connected to the cathode through-Qa.v path which includes` resonant inputy circuit I6' arid-- the resistive loadY impedancel I1, the-latter 'being shunted by a signal carrier bypassffcondenuserV I8;` The signal grid 4- of tube isconnectedte ther anode endbf'loadimpedance Vlg-Whereas; thev cathode end 'of-impedance is connected to condenser V`l2.r yGrid. dis connected to the negative lz terminal of source 9k through'resisto1`f-8.vv Thenumeral |9 -may designatethe resonantoutput circl'iit of any desiredf/typejof predetectornet-v` v work, example, circuits |9vfa'nd may confsistI Lof the tuned primaryY and ,secondary: circuits of thejoutput intermediate ifrequencytransformer 3 )there is ,showna modicatgfi'lvofl'the circuitlv of Fig. l wherein the plate 3; has the impedance l 1 connected 'emmene/uitanerewith, the feedback condenser IZA; connecting the plate end of Aimnegative potential less electrons are permitted to ow to the plate 3 and thereby provide less degenerative signal Voltage acrossv impedance Ill'. f In that case there willbe more electrons flowing to the electrodel 5, than toplate 3. On the other hand as the grid 6 isA adjusted in potential to approach ground potential the ow Vvof electrons to plate 3 is increased, and the degenerative action is also increased. It will, therefo1 'e,J be seen that with maximum negative bias y merid. 6.-in1the vcase or the circuit of Fig. 3, the

volume isiarnaximum.

In FigA thereis shown a modification of the invention wherein in place of an electrostatic control electrode disposed within the tube envelope,1there is employed agmagnetic control field outside ofthe-amp1ifiertube envelope. In this case vthetube 3|Hs provided with a cathode 3| g a signalgrid 32 and a screen grid 33,'. A pair of' anodes, orpla-tes, 311` and, 3,5; may be spaced from i each othenbutlocated in a position tohave electrons from cathode 3|A shiftedfrom one lto the other of'j the plates depending on the intensity of the externakmagnetic control' el-d. The plate A 3'4^may be connectedto the output of the utiliza-v tion network, whereasc plate 35may'be connected" by impedance 36to. the positive terminalfo'f the positive potential; source 37:

As `explainedabove, thesignal grid 32' may be:

maintained' at; a desiredgnegative bias with re- -spectjto ground through the biasing potential tron streamflpwingwithin the -tube to the plates to be@ reduced:

souree 38" and resistor 39,; andcondenser 40 mayy provide the feedback path for the degenerative signal voltage ldeveloped across impedance 36. 'Ihe magnetic control field; mayv be provided'by .,anyl-meanskno-,wnto,thoseskilled in the art; By d way of'illustrationl such a means is, shown as embodying a coil ,50 arranged in series with a' current source5|` and a, variable resistor. 52..

Proper location ,ofcoil 50With'respect to the elecwill enable kthe manipulator readily to shift the electron stream'from oneL ofJ the plates34- to the plate 35.V Assuming, for example, that for maximum volume of the amplifier the electronstream @flows main-ly toyplateK 3- 4g'resistor 52 can beadjusted, to cause the electron stream to shift' to' plate, 35 -when7theoutput o-ffftheamplifier is out-putr circuit'g of 7 theY amplier lis al minimum;

Those skilledA in the art -are fully acquainted with l pedance lto the signal input circuit; The electrede 5A ismconnected to, 'the outputcircuit; Whiley theglaincontrp'l grid 6 is connected by adjustable tap l! 'te D0tni2ia`1-S0ur'9- In* thev presentarraleeieeet asm@ grid .6 assmsa- Hieraan@ andithe degenerative-feedbacky to the signal in= putcircuit-"is aV maximum.- If i desired, a ho-rseshoek-magnet; rotated-'Jmanfually outsidel the tubeAA envelope; rfiayybe-usediI y d Itis to be noted in eachN o fthe circuits yshown that `the direct-current;returnV path forthe signal grid -is through-a fairlyg-high-impedance; thev sig:

suchL vcircuits;--suchan arrangement used with thisanvention willfimproVe-the volume cond trol actionpf-aradio receiver:

'While I have indicated-and described, several rsystems for carrying my invention into effect, it`VY will be apparent-'toene skiil'ed in the art' that my inventio'nisbymomeanslim'ited-to thepa-rticular organizationsshownan'dv-'described,V but'I that manyanodications maybe made 'Without depart= a 'v vhen` the electrony streamv is shiftedgto plate 3 5therr the current ovwinthe ing from the scope of my invention, as set forth in the appended claims.

What I claim is: I

l. In an amplifier of the type including a tube provided with at least an electron emission source, an input electrode and an output electrode; the method including impressing waves upon said input electrode, developing amplified wave voltage at said output electrode, diverting electrons flowing from said source to said output electrode, deriving from the diverted electron flow a wave voltage, combining the derived wave voltage and impressed waves in phase opposition, and concurrently regulating the relative amplitudes of said derived voltage and amplified voltage in opposed senses.

2. In a signal transmission network provided with a tube having an electron emission source, an input electrode, an output electrode, and an auxiliary electrode; the method which includes establishing said input electrode at a negative potential relation to said emission source, impressing signals upon said input electrode, deriving at said output electrode ampliiied signals, deriving a signal voltage from electron flow to said auxiliary electrode, impressing said derived signal voltage upon the input electrode, and controlling the distribution of electrons from said source between said output electrode and said auxiliary electrode.

3. In a signal amplifier, a tube provided with a cathode, a negative signal grid, an output electrode and a positive auxiliary electrode arranged to receive electrons from said cathode, a signal source coupled between the cathode and signal grid, means operatively associated with the auxiliary electrode to develop signal voltage and impress it in degenerative phase upon said signal grid, an output circuit connected to said output electrode, and means for simultaneously controlling the electron iiow to said output electrode and regulating the electronvcurrent flow to said auxiliary electrode thereby to control the magnitude of said degenerative voltage.

4. In a signal amplifier, a tube provided with a cathode, a signal grid, an output electrode and an auxiliary electrode arranged to receive electrons from said cathode, a control electrode disposed in said tube between said output electrode and auxiliary electrode, a signal source coupled between the cathode and signal grid, means operatively associated with the auxiliary electrode to develop signal voltage and impress it in degenerative phase upon said signal grid, an output circuit connected to said output electrode, and means including said control electrode for regulating the electron current iiow to said auxiliary electrode thereby to control the magnitude of said degenerative voltage.

5. In a signal amplifier, a tube provided with a cathode, a signal grid, an output electrode and an auxiliary electrode arranged to receive electrons from said cathode, a signal source coupled between the cathode and signal grid, means operatively associated with the auxiliary electrode to develop signal voltage and impress it in d-egenerative phase upon said signal grid, an output circuit connected to said output electrode, and means for regulating the electron current flow to said auxiliary electrode thereby to control the magnitude of said degenerative voltage, said regulating means comprising a device external of said tube and being constructed to produce a magnetic iield or variable intensity,

6. In a signal amplier, a tube provided with a cathode, a negative signal grid, an output electrode and a positive auxiliary electrode arranged to receive electrons from said cathode, a signal source coupled between the cathode and signal grid, means operatively associated with the auxiliary electrode to develop signal voltage and iinpress it in degenerative phase upon said signal grid, an output circuit connected to said output electrode, and means for simultaneously controlling the electron flow to said output electrode and regulating the electron current flow to said auxiliary electrode thereby to control the magnitude of said degenerative voltage, said iirst named means including an impedance connected between said auxiliary electrode and the cathode, and a path of low impedance to signal voltage connecting the signal grid to a point on said impedance.

7. In combination with a source of audio signal voltage, a tube provided with a catho-de, an output electrode and at least three cold electrodes arranged in succession in the electron stream therebetween, said source being coupled to the cathode and the first of said cold electrodes, an output circuit coupled between the cathode and output electrode, an impedance element in circuit with the second cold electrode, means for establishing the latter and output electrode at a positive potential, means for feeding degeneratively to said rst cold electrode audio voltage developed across said element, and means for varying the potential of the third cold electrode over a range of negative potential values thereby to control the distribution of electrons between the output electrode and said second cold electrode.

8. In combination with a tube provided with at least a cathode, signal input electrode and output electrode, a signal input circuit coupled to the input electrode, a signal output circuit connected to the output electrode, means, responsive to electrons diverted from the electron stream ilowing between cathode and output electrode, for developing signal voltage, means applying the developed signal voltage to said input electrode in degenerative phase relative to the signal voltage from said input circuit, and a single means for simultaneously controlling the magnitude of said electron diversion and the intensity of the electron stream to said output electrode.

9. In combination with a source of audio signal voltage, a tube provided with a cathode, an output electrode and at least three cold electrodes arranged in succession in the electron stream therebetween, said source being coupled to the cathode and the iirst of said cold electrodes, an output circuit coupled between the cathode and output electrode, an impedance element in circuit with the second cold electrode, means for establishing the latter and output electrode at a positive potential, means for feeding degeneratively to said first cold electrode audio voltage developed across said element, means for varying the potential values thereby to control the distribution of electrons between the output electrode and said second cold electrode, said second cold electrode being lconstructed to draw a small electron iiow when said third cold electrode is at minimum negative potential, and a positive screen electrode disposed between said second and third cold electrodes.

TERRY M; SI'IRADER! 2,262,865.-Tewy M. Slwader, West Summit, N. J. VOLUME Co Patent dated Novem NTROL CIRCUITS. ber 18, 1941. Disclaimer filed September 16, 1942, by the assignee, Radio Oorporat/on Qf America. Hereby enters this disclaimer to claims 1, 2, 3, 4, 6, an

d 8 of said patent. [O cal Gazette 0ct0ber Z3, 1942.]

HSCLAIMER 

